The present invention relates to the field of plotting equipment and is concerned more particularly with a color plotter that produces colored images by means of photoexposure techniques.
Automatically controlled plotting equipment is well-known in the art. Such equipment utilizes an instrument such as a drawing pen, and by means of accurately-guided carriage motions translates the instrument relative to a plotting paper or other material in response to programmed command signals to generate an accurate plot of information represented by the signals.
One such plotting instrument disclosed in U.S. Pat. No. 3,330,182, having the same assignee as the present invention, utilizes a photoexposure head that projects a beam of light onto the photosensitive surface of a film. The beam illuminates a spot on the film surface, and by moving the photohead and the spot, the film is exposed along a defined path or plot. When the film is developed a visual representation of the plot is obtained.
A plotting operation as described above may be used to generate drawings, facsimiles of printed circuit boards and other such graphic information. While many such products are adequately defined in black and white, it is desirable in the case of maps, for example, to represent different features by means of different colors. In the past, multicolored maps have been generated from plotters by producing one black and white plot for each color that appears in the map, and then generating printing plates for each such color by conventional photoengraving processes. The plots for each color were individually generated from digitized data and the final product with its various colors was not observable until after the printing process was complete. A direct plot of the map in its various colors is desirable at an earlier stage of development.
Printed circuitboards and integrated circuit chips that consist of multiple layers of conductive, semiconductive and insulating materials are manufactured by photo-resistive plating and etching processes. Drawings or masters used to define the configuration of masks that are employed in generating the various layers of an electrical circuit by these techniques are accurately drawn by computer controlled plotters and are drawn at large scale for proofing purposes before they are reduced to working size. Proofing of the masters for continuity, isolation and registration of the various layers is currently performed by generating transparencies of the circuits in each layer in different colors or in black and white, and then overlaying the transparencies for adjacent layers to examine the registration or isolation of the circuit elements. Color transparencies are preferred to black and white transparencies since the registration or isolation of overlying areas is easier to observe. For example, where two different colors are used to define the electrical components on adjacent layers, the overlapping colors produce a third color that can be readily ascertained by examination. Such color transparencies are currently produced from black and white plots of the masters in a dye process. This process introduces a number of intervening steps between the generation of a black and white plot by an automatically controlled plotter and the final step that yields the color transparencies.
A more rapid proofing of the masks could be obtained if various levels of the circuits could be plotted as a single color composite on photosensitive color film. In such a composite the electrical components of adjacent layers would be represented by different colors, and overlapping portions of the components would be readily identified by a third color that is generated by the combination of colors used to identify each layer.
Still further, with a color plotter, computer generated stereoscopic images of a three dimensional drawing could be plotted on a single piece of sheet material with each image represented in a different one of two complementary colors. When such a drawing is viewed in a stereoscope having appropriate color filters that respectively obliterate the other of the two stereo images, a three dimensional impression of the drawing is obtained.
Accordingly, it is a general object of the present invention to provide a color plotter that offers the capability of generating on a single sheet of material plots in one or a plurality of colors. In addition to the color dimension, it is a further object of the invention to add the dimension of density or shade to plots produced by a plotting apparatus.